But with all the five hopefuls saying no deals have been done, the party's preferential voting system means it's still anyone's game.

Simon Bridges and Amy Adams are believed to have the bulk of the first-round vote. Newshub understands Mr Bridges is a squeak ahead on 23, with Ms Adams on 22.

If none of the contenders get a majority in the first vote, the bottom-placed candidate drops out of contention, and their supporters' second choice votes are distributed among those remaining. This process continues until one candidate has a majority and is crowned leader.

Secret ballot

All five contenders appeared on The AM Show on Monday morning, Mr Bridges the only considering the possibility he may come out on top in the first vote.

"I feel good, but I won't say I've got it in the bag," he told host Duncan Garner.

"The reality is this is a secret ballot - I go in confident tomorrow, but I've got to perform and make sure I sell the vision I have for our caucus and ultimately for New Zealanders."

Simon Bridges.
Photo credit: Getty

Ms Adams says she's "right in it", but thinks it'll go to at least the second round.

"I'm certainly not declaring I'll win on the first ballot, but I think I've got every chance of coming out tomorrow on top."

Amy Adams.
Photo credit: Newshub.

Dark horse Mark Mitchell outright declared he didn't have the numbers to take it out in the first round.

"No, but I've got strong support. To win on the first ballot you need 29. I'm not there."

He said Judith Collins - believed to be in last place with just two votes, one her own - is "almost ready to come over" and back him - perhaps as deputy.

Ms Collins said reports she only had one other backer were a "load of bollocks".

"I have a good dollop of support and I'm really pleased with it. I think we can get through tomorrow [on] the second ballot... In our progressive voting system, you just don't know what's going to happen."

Experience vs rejuvenation

The voting system could help ex-Finance Minister Steven Joyce. His experience and skills are widely respected amongst the National caucus, and could see him perhaps sneak through as everyone's second choice.

Even he initially wanted someone else for the job, before throwing his hat in the ring.

"I'm generally not the sort of person who throws themselves at the front. I'm passionate about New Zealand's future... but at the end of the day I've never put myself forward."

Steven Joyce.
Photo credit: Newshub.

Until now. He says a lot of people "came out of the woodwork" and urged him to stand.

"They thought I would be the best to lead the party, and most importantly lead the country, post-2020."

He's open to a "weaponised" Ms Collins taking the deputy role. Ms Collins said she liked Mr Joyce better than Bill English as Finance Minister, and would be open to being his deputy.

"Who gave me the most money for police, corrections, everything else I needed? They were both very good. I think that Steven is probably the better for me to deal with in many ways, and was very, very attuned to the electorate - like I am."

Coalition problems

To get into Parliament again, it's likely National will need a coalition partner - the lack of one is what saw them fall into Opposition last year, despite being the largest party in Parliament.

Asked whether he'd rather cut a deal with Winston Peters' New Zealand First or the Greens, Mr Bridges opted for the latter - on one condition.

"It does depend on who the Greens are, but I think if they're a true environment party, the Greens."

Mark Mitchell.
Photo credit: Facebook/The National Party

The Greens back free education, so might run into difficulty should Mr Mitchell hold the reins - saying he'd cut the Government's free tertiary education policy without hesitation if the money was needed elsewhere.

"If the country needed investment into our health system or the money needed to be put somewhere else and there was a clear need, then I would definitely look at reversing a third year of free tertiary education, without a doubt. If the economy was going well - and I don't think it will be - then I would look at it. This tertiary policy really is not very good."